It is known to transmit Power over Data Lines to remote power equipment. Power over Ethernet (PoE) is an example of one such system. In PoE, limited power is transmitted to Ethernet-connected equipment (e.g., VoIP telephones, WLAN transmitters, security cameras, etc.) from an Ethernet switch. DC power from the switch is transmitted over two or more twisted wire pairs in the standard CAT-n cabling. One or more of the wire pairs also transmit differential data signals, since the DC common mode voltage does not affect the data. In this way, the need for providing any external power source for the Powered Devices (PDs) can be eliminated.
A newer technology is Power over Data Lines (PoDL) where power is transmitted over a single, twisted wire pair along with the differential data. As of the date of this disclosure, the IEEE is in the process of developing a standard for PoDL as IEEE 802.3bu. PoDL may be more flexible than PoE and, since it requires just one wire pair, is likely to become a popular technique, especially in automobiles.
It is envisioned that PoDL applications will require some manner of isolation between the PD ground and the PSE ground in order to prevent the formation of or minimize the effects of ground loops. The grounds are the respective reference nodes for the PSE and PD and are not necessarily absolute grounds or equal to each other. While failure of the PSE ground to PD ground isolation may not result in outright functional failure of the PoDL link, the resulting current flow (leakage current) may substantially degrade the integrity of the Ethernet data. Hence the ability to detect a failure in the isolation between the PD ground and PSE ground is important in order ensure data integrity in a PoDL Ethernet link.